Ensure that the web contents trying to access native VR Shell is the webcontents we created.

chrome/browser/android/vr_shell/vr_shell.cc

Index: chrome/browser/android/vr_shell/vr_shell.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell.cc b/chrome/browser/android/vr_shell/vr_shell.cc
index 9e9b090a4b6aa4a9a5f82f0a0159b504a4301d1a..364b65b8ed4a3b061f54e859cab8a98ac2fa9575 100644
--- a/chrome/browser/android/vr_shell/vr_shell.cc
+++ b/chrome/browser/android/vr_shell/vr_shell.cc
@@ -488,9 +488,12 @@ void VrShell::OnResume(JNIEnv* env, const JavaParamRef<jobject>& obj) {
   gvr_api_->ResumeTracking();
 }
 
-base::WeakPtr<VrShell> VrShell::GetWeakPtr() {
-  // TODO: Ensure that only ui webcontents can request this weak ptr.
-  if (g_instance != nullptr)
+base::WeakPtr<VrShell> VrShell::GetWeakPtr(
+    const content::WebContents* web_contents) {
+  // Ensure that the WebContents requesting the VrShell instance is the one
+  // we created.
+  if (g_instance != nullptr &&
+      g_instance->ui_cvc_->GetWebContents() == web_contents)
     return g_instance->weak_ptr_factory_.GetWeakPtr();
   return base::WeakPtr<VrShell>(nullptr);
 }